Partially depleted silicon-on-insulator (PDSOI) transistors are a top choice for low-power radio frequency (RF) switch devices, especially in mobile applications where price, performance, and power consumption are key elements. However, PDSOI transistors are challenged when handling larger signals. In particular, large signal performance in PDSOI switches is affected by charge accumulation in a quasi-neutral region of the body of the PDSOI transistors. Charge accumulation may result in hot-carrier accumulation, excess gate-induced drain leakage (GIDL), negative transconductance, loss of gate control, hysteresis, etc. These issues may be generally referred to as floating body effect (FBE).
In an n-channel metal oxide semiconductor field effect transistor (NMOS) device, the most common way to suppress hot-carrier accumulation related to FBE is to create a discharge path for the accumulated charges. A negative DC voltage is applied to the gate of the NMOS in order to turn it off while the body is kept floating. Therefore, in order to bleed the accumulated charges and turn off the parasitic bipolar junction transistor (BJT) that forms across the NMOS, the negative DC voltage needs to be transmitted to the body.
Several techniques were developed to perform this task. These techniques include connecting the body to the gate using diodes or diode-connected FETs, or even applying a negative DC voltage equal to the gate voltage using a large resistor (referred to as “resistive body contact”). While these techniques may bleed the hot-charges, turn off the parasitic BJT, and help suppress harmonics generated by the off FETs; they may also adversely affect operation of the device in other ways.
For example, the diode-connected FET may transmit the negative DC voltage applied to the gate plus a DC threshold voltage, Vth, which corresponds to the device threshold voltage. This may compromise efficiency of the charge-bleeding mechanism.
For another example, the resistive body contact may be able to apply the appropriate negative DC voltage to the body of the device; however, the resistor may be associated with extra insertion loss and decreased performance with respect to intermodulation distortion (IMD) and second-order harmonics.